The ongoing concept work on future mobile communication systems reveals significant changes to the mobile network architecture. In order to make networks more efficient, provide higher data rates and throughput, and reduce latency in the network, new radio access technologies and network architectures are investigated, as e.g., in the context of UMTS LTE (Universal Mobile Telecommunications System Long Term Evolution).
At present, a UMTS network consists of three interacting domains; Core Network (CN), UMTS Terrestrial Radio Access Network (UTRAN) and User Equipment (UE), as shown in FIG. 1.
The main function of the core network is to provide switching, routing and transit for user traffic. The core network also contains the databases and network management functions. At present, the core network for UMTS is based on the GSM network with GPRS.
The UTRAN provides the air interface access method for User Equipment. It is subdivided into individual radio network systems (RNSs), where each RNS is controlled by a Radio Network Controller (RNC). The RNC is connected to a set of base stations (Node-B), each of which can serve one or several cells. The functions of the RNC are: radio resource control, admission control, channel allocation, power control settings, handover control, macro diversity, ciphering, segmentation/reassembly, broadcast signalling and open loop power control.
The functions of the base station (Node-B) are Air interface Transmission/Reception, Modulation/Demodulation, CDMA Physical Channel Coding, Micro Diversity, Error handling and closed-loop power control.
Regarding the evolved architecture in UMTS LTE (Long Term Evolution), FIG. 2 is a schematic illustration of the repartition of tasks in UMTS LTE. The eNode B handles Radio Resource Management: Radio Bearer Control, Radio Admission Control, Connection Mobility Control, Dynamic Resource Allocation (scheduling). The Mobility Management entity (MME) handles the distribution of paging messages to the eNBs, while the User Plane Entity (UPE) handles IP Header Compression and encryption of user data streams, termination of U-plane packets for paging reasons and switching of U-plane for support of UE mobility.
A more detailed description of the UMTS standard and its evolution may be found in the standardization documents of 3GPP, in particular the technical reports 3GPP TS 23.002 V7.1.0(2006-03), 3GPP TSTS 25.401 V3.0.0 (1999-10) and 3GPP TR 25.912 V7.0.0 (2006-06).
One direction in the long term evolution of UMTS networks is the increasing assignment of additional protocol functionality to the base station (Node-B), such as scheduling of radio resources, allocation of User Equipments (UEs), evaluation of measurements, radio bearer control, admission control and connection mobility control.
One the other side, operational costs of the network are still very much determined by the transport costs inside the network, e.g. between base station and other network nodes. Thus, data rates that could be possible with a given air interface design cannot be reached, because the bottleneck is behind the base station.
In this respect, existing networks for GSM, UMTS and also the planned extensions of UMTS currently only foresee one mode of operation involving a transfer of data via a core network connection.
Transfer of high data rates in current mobile networks may be very costly for the operator due to high backhaul/transport costs within the network. If the operator wants to make use of the capacity available on the air interface (100 Mbps planned in LTE, even more in 4G systems), the operator needs to provide according capacity within the network.
As another disadvantage, routing the communication via several network elements can introduce delays which are increasing the latency experienced by the user. However, low latency is one of the most important criteria for future data services (e.g., gaming, VoIP). There is currently little means for the operator to use the existing network architecture in a more flexible way.